The invention relates generally to measurement of transverse acceleration, also known as load balloting, along a gun barrel. In particular, the invention relates to techniques to measure load balloting using X-ray imagery.
Superficially, the dominant force in gun-launched projectiles appears to be axial compression (i.e., setback) of the projectile upon launch. Determination of this force is straightforward because the chamber pressure can be calculated from the propellant used to launch the projectile. Additionally, the axial acceleration of the projectile can also be calculated by measuring the muzzle velocity of the projectile.
Axial acceleration is not the only interior ballistics acceleration the designer must take into account. Transverse accelerations (commonly referred to as balloting) within the gun barrel can occur and have been known to cause structural failures within the projectile if the accelerations are severe. Even when not sufficiently severe to cause projectile failure, these accelerations can affect the transition phase of the projectile during exit from the muzzle to begin ballistic flight.
In-bore balloting causes can be produced by a variety of reasons; lack of barrel straightness, bore irregularities, variations in projectile center of mass, etc. Regardless of the cause, the effects can be severe and undesirable. Unlike axial acceleration, balloting is not easily calculated by simple analytical techniques, because its causes are not simple and can change as the gun barrel wears or due to differences in projectile manufacture. Conventionally, in-bore balloting is not easily measured.